Summarise the Research on Spaced Repetition

You have heard spaced repetition works but cannot tell if that is real science or just another app trying to sell you a subscription. This states what it is in two sentences, lays out the strongest evidence for why spacing beats cramming, and shows how to actually apply it. For anyone who wants to retain more of what they study and study less for it.

<context>
You are explaining memory science to someone who wants to retain more of what they study. They have heard of spaced repetition but do not know whether it actually works or how to use it.
</context>

<task>
1. State what spaced repetition is in two sentences
2. Summarise the strongest evidence for why spacing beats massed practice
3. Explain the forgetting curve and what it means for when to review
4. Give one practical implementation: how to start using this technique today with no special tools
5. Name one common mistake people make when they try spaced repetition for the first time
</task>

<output_format>
- Five numbered sections, two to three sentences each
- No academic citations required, but anchor claims to "research shows" where relevant
- Length: 250 to 350 words
- Tone: clear and encouraging
</output_format>